Keep huge finite values finite in round_to (#2309)

Found while testing crates/geom/src/transform.rs:58 (round_to), used by crates/engine/src/automation/inspect.rs:517 (round)

Co-authored-by: Claude Haiku 5.5 <noreply@anthropic.com>

crates/geom/src/tests.rs

@@ -306,6 +306,12 @@ fn round_to_handles_large_precision_without_changing_finite_values() {
     assert_eq!(round_to(1.23456, 2), 1.23);
 }
 
+#[test]
+fn round_to_keeps_huge_finite_values_finite() {
+    assert_eq!(round_to(1e307, 2), 1e307);
+    assert_eq!(round_to(-1e307, 2), -1e307);
+}
+
 #[test]
 fn reverse_subpaths_preserves_open_and_closed() {
     let mut open = BezPath::new();

crates/geom/src/transform.rs

@@ -60,6 +60,11 @@ pub fn round_to(v: f64, digits: i32) -> f64 {
     if v.is_finite() && !f.is_finite() {
         return v;
     }
-    let r = (v * f).round() / f;
+    let scaled = v * f;
+    if v.is_finite() && !scaled.is_finite() {
+        // Too large to have a fractional part at this scale; already whole.
+        return v;
+    }
+    let r = scaled.round() / f;
     if r == 0.0 { 0.0 } else { r }
 }